European patent application of the present applicant published under publication number EP 2 770 637 A1 (the contents of which are incorporated herein by reference)—hereinafter the '637 publication—describes a piezoelectric switch circuit having at least one piezoelectric sensor element. FIG. 10 thereof has been redrawn as FIG. 1 of the present application and illustrates a piezoelectric switch circuit having two piezoelectric sensor elements.
The piezoelectric sensor elements of the piezoelectric switch circuit of the '637 publication and also that shown in FIG. 1 may be used not only to detect a signal resulting from bending of the piezoelectric sensor element due to it being subject to a force that results from pressure or force exerted (such as by a human finger) on a surface to which the piezoelectric sensor element has been attached from below the surface, but also to produce a haptic signal that can be sensed (such as by the human finger) through the surface.